The main objectives of the proposed research are the following: 1) to investigate whether changes in head position with respect to gravity can modify the spontaneous activity of ascending spinoreticular neurons; 2) to study the synaptic organization of the responses of precerebellar reticular neurons (located in the lateral reticular nucleus, LRN) to natural stimulation of macular receptors, in particular to find out whether the responses depend upon direct monosynaptic excitation of LRN neurons induced by vestibuloreticular volleys or whether they result from vestibulospinal excitation of ascending spinoreticular neurons projecting to the LRN; 3) to study the possible convergence and interaction between somatic afferent volleys originating from neck proprioceptors and those originating from macular receptors, within precerebellar and cerebellar nuclear structures which are known to be involved in the fine control of posture and movements; 4) to investigate at the electron microscope the synaptic organization of the efferent projections originating from the vestibular nuclei in the toad; 5) to investigate the basic mechanisms involved in REM (rapid eye movements) sleep. It has been postulated that serotonin (5-HT) is involved in the "triggering" of REM sleep episodes. Since we have shown previously that the bursts of REM depend upon rhythmic changes in the vestibulooculomotor discharge due to activation of a cholinergic reticular mechanism, experiments will be performed to find out whether the activity of this cholinergic reticulo- vestibular system can be modified following manipulation of the synthesis, release and metabolism of monoamines, in particular serotonin.